The present invention relates to image forming apparatus, and in particular, to the control of the surface potential of an image bearing member.
It is known in the art to control the surface potential of an image bearing surface. For example U.S. Pat. No. 4,512,652, commonly assigned discloses a control in a electrophotographic printing machine wherein the charging current for the photoconductive member of the printing machine is a function of the time elapsed between successive operating cycles of the machine and a constant characterizing the photoconductive member. U.S. Pat. No. 4,348,099, also assigned to the same assignee as the present invention, discloses a control loop to adjust the charging member in an electrophotographic machine. In particular, an electrometer measures the photoreceptor surface voltage level, compares it to a reference, and determines a voltage adjustment necessary for the charging cort to maintain a consistent photoreceptor surface voltage level.
In addition, U.S. Pat. No. 4,355,885 discloses an image forming apparatus provided with a surface potential control device wherein a magnitude of a measured value of a surface potential sensor and aimed potential value are discriminated and an output from an output device such as an exposure device is increased or decreased for a predetermined value by the discriminated output. The measuring, discriminating, adding and subtracting operations are repeated to control the surface potential within a predetermined range. U.S. Pat. No. 4,484,811 discloses an apparatus for forming an image on a recording member wherein in consecutive latent image forming cycles, a non-imaged area present between two consecutive latent images is exposed to a predetermined amount of light to form an electrostatic image, the potential of which is measured to control the development of a latent image.
In the prior art, it is known that certain types of image bearing members exhibit cyclic instability between the initial cycles of the machine particularly at machine start-up, primarily due to ambient conditions such as temperature, humidity and time period since the last shut down of the machine. In such machines, the charging member supplying the same current may produce a potential on the image bearing member that differs by as much as 250 volts between cycles.
It is common in such control loops to measure the voltage of the image bearing member against a reference and, in response, provide corrective feedback. Such control loops, however, adapt to measured conditions but do not predict correct parameters such as charging current based upon accumulated data.
To compensate for the above-identified difficulties, it would be desirable to provide a control that compensates for cyclic instability in the image bearing surface and does not merely adapt to measured and determined error signals.
It is an object of the present invention, therefore, to provide a new and improved image bearing surface control and in particular a control that compensates for cyclic instability in the image bearing member and also provides both a predictive and adaptive feedback control.